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man: document ShowStatus and SetShowStatus()

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SetShowStatus() was added in order to fix #11447. Recently, I ran into
the exact same problem that OP was experiencing in #11447. I wasn’t able
to figure out how to deal with the problem until I found #11447, and it
took me a while to find #11447.

This commit takes what I learned from reading #11447 and adds it to the
documentation. Hopefully, this will make it easier for other people who
run into the same problem in the future.
This commit is contained in:
Jason Yundt 2024-09-17 14:00:26 -04:00 committed by Lennart Poettering
parent fc5037e7d7
commit dfb3155419
3 changed files with 40 additions and 7 deletions
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28
man/org.freedesktop.systemd1.xml
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@ -593,8 +593,6 @@ node /org/freedesktop/systemd1 {
<!--method GetJobBefore is not documented!-->
<!--method SetShowStatus is not documented!-->
<!--method ListUnitsFiltered is not documented!-->
<!--method ListUnitsByPatterns is not documented!-->
@ -673,8 +671,6 @@ node /org/freedesktop/systemd1 {
<!--property ConfirmSpawn is not documented!-->
<!--property ShowStatus is not documented!-->
<!--property DefaultStandardOutput is not documented!-->
<!--property DefaultStandardError is not documented!-->
@ -1362,6 +1358,24 @@ node /org/freedesktop/systemd1 {
<para><function>ResetFailedUnit()</function> resets the "failed" state of a specific unit.</para>
<para><function>SetShowStatus()</function> configures the display of status messages during bootup and
shutdown. The <varname>mode</varname> parameter can be set to any value that's valid for the
<varname>systemd.show_status</varname> kernel parameter. For more information about
<varname>systemd.show_status</varname>, see
<citerefentry project="man-pages"><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
The <varname>mode</varname> parameter can also be set to an empty string. When <varname>mode</varname>
is set to an empty string, <function>SetShowStatus()</function> will reset
<varname>ShowStatus</varname> back to its original value. You can use
<function>SetShowStatus()</function> create a service that does something like this:
<orderedlist>
<listitem><para>Send a D-Bus message that will turn off status messages.</para></listitem>
<listitem><para>Block until a reply to that message is received.</para></listitem>
<listitem><para>Print multiples lines without being interrupted by status messages.</para></listitem>
<listitem><para>Send a D-Bus message that will reset <varname>ShowStatus</varname> back to its
original value.</para></listitem>
</orderedlist>
</para>
<para><function>ResetFailed()</function> resets the "failed" state of all units.</para>
<para><function>ListUnits()</function> returns an array of all currently loaded units. Note that
@ -1788,6 +1802,12 @@ node /org/freedesktop/systemd1 {
<para><varname>Environment</varname> encodes the environment block passed to all executed services. It
may be altered with bus calls such as <function>SetEnvironment()</function> (see above).</para>
<para><varname>ShowStatus</varname> encodes systemd's current policy for displaying status messages
during bootup and shutdown. Its value can be any valid value for the
<varname>systemd.show_status</varname> kernel parameter (see
<citerefentry project="man-pages"><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
It may be altered using <function>SetShowStatus()</function> (see above).</para>
<para><varname>UnitPath</varname> encodes the currently active unit file search path. It is an array of
file system paths encoded as strings.</para>

7
man/systemd.exec.xml
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@ -3001,7 +3001,12 @@ SystemCallErrorNumber=EPERM</programlisting>
<para><option>tty</option> connects standard output to a tty (as configured via <varname>TTYPath=</varname>,
see below). If the TTY is used for output only, the executed process will not become the controlling process of
the terminal, and will not fail or wait for other processes to release the terminal.</para>
the terminal, and will not fail or wait for other processes to release the terminal. Note: if a unit
tries to print multiple lines to a TTY during bootup or shutdown, then there's a chance that those
lines will be broken up by status messages. <function>SetShowStatus()</function> can be used to
prevent this problem. See
<citerefentry project="man-pages"><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details.</para>
<para><option>journal</option> connects standard output with the journal, which is accessible via
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>. Note

12
man/systemd.xml
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@ -568,7 +568,11 @@
<listitem><para>Enables display of status messages on the
console, as controlled via
<varname>systemd.show_status=1</varname> on the kernel command
line.</para></listitem>
line.</para>
<para>You may want to use <function>SetShowStatus()</function> instead of
<constant>SIGRTMIN+20</constant> in order to prevent race conditions. See
<citerefentry project="man-pages"><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
@ -579,7 +583,11 @@
controlled via
<varname>systemd.show_status=0</varname>
on the kernel command
line.</para></listitem>
line.</para>
<para>You may want to use <function>SetShowStatus()</function> instead of
<constant>SIGRTMIN+21</constant> in order to prevent race conditions. See
<citerefentry project="man-pages"><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>